It's similar like XZ compressed files.  For the simplicity, both XZ
and ZSTD tests are done in a single function.  The format is specified
via $COMPRESS_FORMAT and the compression function is pre-defined.

Link: https://lore.kernel.org/r/20210127154939.13288-5-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220421152908.4718-6-tiwai@suse.deSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>